In the related art, there is a known heat exchanger having a hollow fiber membrane layer which is configured to include a plurality of hollow fiber membranes so as to form an overall shape of a cylindrical body. A hollow fiber sheet disclosed in PTL 1 can be applied to the hollow fiber membrane layer forming the cylindrical body shape. In the hollow fiber sheet disclosed in Japanese Registered Utility Model No. 2579299, the plurality of hollow fiber membranes are disposed in substantially parallel to each other so as to be the woof, and the woof is woven together with the warp, thereby forming a bamboo blind-shaped sheet. Such a bamboo blind-shaped hollow fiber sheet can serve as the hollow fiber membrane layer by being caused to have a cylindrical body shape. In this case, each of the hollow fiber membranes of the hollow fiber sheet is disposed substantially parallel to the central axis of the cylindrical body.
In the heat exchanger including the hollow fiber membrane layer having such a configuration, when the heat medium passes through the inside of the hollow fiber membrane, the passing distance thereof for obtaining sufficient heat exchange is not ensured. Therefore, in order to improve the heat exchanger effectiveness, there is a need to increase the number of times of winding each of the hollow fiber membranes by winding the hollow fiber membrane about the central axis of the cylindrical body. However, as the number of times of winding the hollow fiber membrane increases, the overall length of the hollow fiber membrane becomes elongated. In proportion thereto, there is a problem of an increase of a pressure loss of the heat medium passing through the inside of the hollow fiber membrane. Accordingly, there is a concern that the heat exchanger effectiveness deteriorates.
In addition, in a case where a heat exchanger using a bamboo blind-shaped hollow fiber sheet is applied to an oxygenator for use in cardiac support, gaps among and between the hollow fiber membranes can be configured to allow blood to pass through.
However, as the number of times of winding each of the hollow fiber membranes increases, the total volume of the gaps among and between the hollow fiber membrane increases. As a result thereof, the quantity of blood passing through the gaps, that is, a blood filling amount (i.e., blood volume contained within the oxygenator) also increases, and thus, the burden to a patient becomes significant.